Modulating system and method



131F111 1931- H. E. OVERACKER 1,800,471

MODULATING SYSTEM AND METHOD Filed April 4, 192's PIE. 1.

H. [T Ovaracker WW M ATTOR EYS res1stance of a clrcultelement unlformly at Patented Apr. 1 4, 1931 UNITED STATES PATENT OFFICE HORACE E. OVERACKER, OF IALO ALTO, CALIFORNIA, ASSIGNOR TO FEDERAL TELE GRAPH COMPANY, OF SAN FRANCISCO, CALIFORNIA, A CORPORATION OF CALI- FORNIA Application filed ApriI 4,

in radio receiving systems. a

An object of the invention. 1s to vary the a periodic rate without resorting to the use of a device having moving contacts or any other, mechanically moving parts.

Another object of the invention is to modulate a received continuous wave at an audible rate in asimple and effective way whereby the signal may be made perceptible.

My system and method may be outlined briefly as utilizing an electron relay having the usual input and output circuits,which are arranged to pass radio or carrier frequency energy; Connected across points of different potentialof thesecircuits there is a gas discharge tube having cold electrodes. This gas discharge tube is excited in such'a manner that its resistance is repeatedly broken down,

4 with a result that the resistance across the two points of different potential is repeatedlyvaried between finite and infinite values. In the preferred form of my invention the system is incorporated in a radio receiver in which the electrone relay has its input cirgcu'it associated witha suitable source of signal energyof carrier frequency.

Referring to the drawing Figure, 1 is a circui diagram illustrating one 'forrnof my'system and method.v

Fig. '2 is another'circuit diagram illustrating another form of my system and 3 method.

To describe my invention more specifically,

in Fig. 1 I have shown a suitable form ofelectron relay 11 capable of repeating signal energy. of carrier or radio frequencies, Theconventional relay shown by way of example utilizes a cathode 12 of the filamentary type,

I anode or-plate 13 and, grid or control element Some form ofradio frequency circuit is associated with the input of relay 11, as for example an inductance 16 tuned as by 1 means of variable capacitance 17. Since in the preferred embodiment of my invention I utilize relay 11 for integrating signals, I have shown a grid condenser 18. Asuitable grid MODULATING SYSTEM AND METHOD 1928. Serial No. 267,257.

leak resistance 19 is also shown connected between the'grid and cathode.

In order to provide regeneratlon of energy repeated by the relay 11, I preferably provide a suitable feed back circuit such as is provided byan inductance 21 included in the plate circuit 13, and which'is inductively coupled to inductance 16. For controlling the degree of regeneration I hav'eshown a variable capacitance 22 connected in series with inductance pressed upon'a further integrating device before being translated. As explained above,

since in my preferred system I utilize grid condenser 18 and grid leak 19, the relay 11 serves both as an integrating and an amplifying device. To secure further amplification of the integrated signals however I prefer to couple a suitable audio frequency amplifier 23 to the outputof relay 11 and to supply a suitable translator 24 from the output-of this amplifier. As a suitable means for coupling together relay 11 and amplifier 23, I have shown an audio frequency trans-v former 25having its primary winding. con nected in series with B battery 26 and the output circuit of relay -11. A suitable radio frequency choke 27 is preferably inserted between transformer 24 and the inductance21.

As a suitable source of signal energy of carrier frequency, I may. either directly couple the input of relay 11 to a carrier wave transmission line or to a radio antenna, or the coupling may be effected thru one or more stages of radio frequency amplifiers. In the drawing for simplicity Ihave shown a radio antenna 28 connected to the high potential 7 side of the input of relay 11', thru the series tuning condenser 29.

Forefl'ecting modulation of signal energy repeated thru relay 11, I preferably utilize a gas discharge tube 31 having the usual cold cathode and anode electrodes 32 and 33. Gas

discharge tubes are well known in the art and consist of anode and cathode electrodes operated at normal temperatures and enclosed within an evacuated vessel. The vessel contains one or more readily ionizable gases such as neon, argon, helium, zenon, hydrogen and the like, at relatively low pressure. Tubes of this type have practically infinite resistance or impedance until the potential across their electrodes is increased above a certain critical value, after which the resistance is broken down and a current flow occurs. After a current flow has been initiated the resistance of the tube is relatively low.

There are a number of ways in which a gas discharge tube may be excited so that its resistance is repeatedly broken down at a rate which is at least a musical frequency. For example it may be excited by a pulsating or alternating current to repeatedly break down the resistance of the tube at a freque'ncyequal to the current impulses, or it may be excited from a direct current source in series, with a high resistance. For simplicity I have shown the latter arrangement which conslsts of a suitable source. of direct current such as a battery 34 connected across ing determined by the characteristics of the exciting circuit and by the characteristics of the gas discharge tube 31. Ingeneral it may be stated that the frequency may be controlled by varying resistance 86, by placing a variable capacitance across the electrodes of tube 31, or by placing such a capacitance in shunt with resistance/36. I have shown an adjustable capacitance shunted across resistance 36, as for example by provldmg a fixed condenser 37 shunted, by a 7 variable condenser 38. I Vith this arrange- 11161117. of .a fixed and variable condenser, closer control may be had than by using a single var able condenser.

For cooperatively associatingthe gasdischarge tube with the remainder of the system, I preferably connect the same across two points of different potential of the radio frequency circuits of relay 11. For exam ple two such points of different potential are formed by the terminals of variable condenser 22, which in that form of the invention shown in Fig. 1 has been shown as con nectedto the gas discharge tube 31 thru leads. 39 and 41. In order to prevent audio frequency impulses set up in the exciting circuit from tube 31 from being fed back into the circuit of relay 11', I preferably jjil'ize blocking condensers 42 and 43' 'ii eft d in series with lead 41, this lead being connected to the high potential side of condenser 22. This arrangement is made more effective by the use of a radio frequency choke 44 which will pass audio frequency impulses set up by tube 31, but which Will act as a choke for radio frequency currents. As the cathode of relay 11 and therefore likewise lead 39 is preferably grounded as by means of ground connection 45, I also preferably utilize a radio frequency choke 4fi-inseries with the anode of tube 31 in order to prevent radio frequency currents from passing to ground through battery 34.

7 With the system as explained above, it 80 will be apparent that Whenth'e'tube 31 is in operating condition, that is 7 when its resistance'is being broken'down at periodic intervals by its exciting circuit, "the circuit which includes this tube and which is (3011 985 necte'd across the points of different .potential located at opposite sides of variable con denser 22, will have its values ofresistance periodically varied. In other words the arrangement is substantially equivalent'to pe- 'eo riodically bypassing the radiofrequency currents in condenser 22 thru a resistance. As

a resultthe signal currentsbeingrepeated by relay ll are modulated by frequency cor- I responding to the frequency of operation of gas discharge tube 31. Such modulation re sults chiefly from the repeated'vari'ation of the resistance component of the radio frequency circuits, although to a certain degree it is caused by the det-uning effect of- 1 the low impedance path provided thru the gas discharge tube. For reception of continuous wavetelegraphic signals, I prefer to operate the gas discharge tube at an audi-V. ble or tone frequency so that "energy of this" tone frequency is repeated thru amplifier '23 and impressed upon the translator 24. Because of the manner in which the 'audio fire-- quency impulses set up in the exciting circuit of tube 31 are prevented from passingllo into the circuits of relay 11, no currents of tone frequency are received bytlietranslator during intervals when no signal energy is beingreceived, r f V V .7

I' have found um'wah this receiving 'sys-"" 5 tem, the relay 11 canbe operated in far more sensitive condition than without the use of such a modulating device. In other words with my modulating deuc i11pperati'on,the, amount of regeneration may be greatly i creased without causingjthei ei yto spin-aver into local oscillation. Whiletlfig mode of operation is believed novel. as; applied to my system, it is to be understood that the eye, tern is practically o erative, for the recf 'pf tion of signals without utilizingj'freg'enerative action to 'a greater degree "than would be resent if my modulation device were not employed. Y I r l I In Fig. 2 I'have shciv'ii'a ramification of M13) my system and method, in which the gas discharge tube is connected to two other different points of potential of the circuits for relay 11. In this case the two points are located along the inductance 16 so that when the resistance of tube 31 is broken down the effect is to place a radio frequency path having a substantial resistance component in shunt with a portion of inductance 6. In

this case I prefer to dispense with the choke 44 and a single stopping condenser 42 is inserted between the inductance 16 and gas discharge tube 31, as the turns of inductance 16 across which the gas discharge tube is connected presents a short circuit path of low impedance for relatively low frequency currents originating in the gas discharge tube circuit. Choke 46 functions in the same manner as choke 46 of Figure 1.

I claim:

In a carrier wave receiving system, a source of signal energy of carrier frequency, an electron relay detector having a radio frequency input circuit adapted to receive energy from said source, a radio frequency circuit associated with the output of said relay and adapted to feed energy into said input circuit whereby said relay is adapted to operate regeneratively, a gas discharge tube having cold electrodes connected across points of different potential of said circuit, and means for exciting said gas discharge tube whereby it is caused toperiodically vary its ref sistance.

In testimony h d whereof, I have hereunto set my an HORACE E. OVERACKER. 

